A common situation in optical measuring systems is to encounter a very high bandwidth intensity modulation on an optical signal. This intensity variation could be the result of a high bandwidth modulator, or it could be the result of some sort of physical process that is to be characterized. Optical fibers easily support multiple terahertz levels of bandwidth, since the optical frequency itself is so high.
A challenge in characterizing such optical signals is the difficulty of directly measuring intensity variations at picosecond response times or faster. Photo detectors are usually based on semiconductor devices, and a finite time needed for free carriers to enter and leave the optically active areas. As a result, responses for practical devices are usually limited to bandwidths of 100 GHz or less. Another problem is the increasing difficulty of building RF waveguides and electronics that operate at speeds of 100 GHz and higher in an economical fashion.
There is a need for an efficient and inexpensive sampling device to detect such variations in intensity over a wide bandwidth.